Dynamics and Constraints of the Massive Gravitons Dark Matter Flat Cosmologies

We discuss the dynamics of the universe within the framework of Massive Graviton Dark Matter scenario (MGCDM) in which gravitons are geometrically treated as massive particles. In this modified gravity theory, the main effect of the gravitons is to alter the density evolution of the cold dark matter component in such a way that the Universe evolves to an accelerating expanding regime, as presently observed. Tight constraints on the main cosmological parameters of the MGCDM model are derived by performing a joint likelihood analysis involving the recent supernovae type Ia data, the Cosmic Microwave Background (CMB) shift parameter and the Baryonic Acoustic Oscillations (BAOs) as traced by the Sloan Digital Sky Survey (SDSS) red luminous galaxies. The linear evolution of small density fluctuations is also analysed in detail. It is found that the growth factor of the MGCDM model is slightly different ($\sim1-4$) from the one provided by the conventional flat $\Lambda$CDM cosmology. The growth rate of clustering predicted by MGCDM and $\Lambda$CDM models are confronted to the observations and the corresponding best fit values of the growth index ($\gamma$) are also determined. By using the expectations of realistic future X-ray and Sunyaev-Zeldovich cluster surveys we derive the dark-matter halo mass function and the corresponding redshift distribution of cluster-size halos for the MGCDM model. Finally, we also show that the Hubble flow differences between the MGCDM and the $\Lambda$CDM models provide a halo redshift distribution departing significantly from the ones predicted by other DE models. These results suggest that the MGCDM model can observationally be distinguished from $\Lambda$CDM and also from a large number of dark energy models recently proposed in the literature.Comment: Accepted for publication in Physical Review D (12 pages, 4 figures

An Exact Approach to Early/Tardy Scheduling with Release Dates

In this paper we consider the single machine earliness/tardiness scheduling problem with di?erent release dates and no unforced idle time. The problem is decomposed into a weighted earliness subproblem and a weighted tardiness subproblem. Lower bounding procedures are proposed for each of these subproblems, and the lower bound for the original problem is then simply the sum of the lower bounds for the two subproblems. The lower bounds and several versions of a branch-and-bound algorithm are then tested on a set of randomly generated problems, and instances with up to 30 jobs are solved to optimality. To the best of our knowledge, this is the first exact approach for the early/tardy scheduling problem with release dates and no unforced idle time.scheduling, early/tardy, release dates, lower bounds, branch-and-bound

Heuristics for the Early/Tardy Scheduling Problem with Release Dates

In this paper we consider the single machine earliness/tardiness scheduling problem with di?erent release dates and no unforced idle time. We analyse the performance of several dispatch rules, a greedy procedure and a decision theory local search heuristic. The dispatch rules use a lookahead parameter whose value must be specified. We perform some experiments to determine an appropriate value for this parameter. The use of dominance rules to improve the solutions obtained by these heuristics is also considered. The computational results show that the use of the dominance rules can indeed improve the solution quality with little additional computational e?ort. To the best of our knowledge, this is the first analysis of heuristic performance for the early/tardy scheduling problem with release dates and no unforced idle time.scheduling, early/tardy, release dates, heuristics

Improved Lower Bounds for the Early/Tardy Scheduling Problem with No Idle Time

In this paper we consider the single machine earliness/tardiness scheduling problem with no idle time. Two of the lower bounds previously developed for this problem are based on lagrangean relaxation and the multiplier adjustment method, and require an initial sequence. We investigate the sensitivity of the lower bounds to the initial sequence, and experiment with di?erent dispatch rules and some dominance conditions. The computational results show that it is possible to obtain improved lower bounds by using a better initial sequence. The lower bounds are also incorporated in a branch-and-bound algorithm, and the computational tests show that one of the new lower bounds has the best performance for larger instances.scheduling, early/tardy, lower bound

Improved Heuristics for the Early/Tardy Scheduling Problem with No Idle Time

In this paper we consider the single machine earliness/tardiness scheduling problem with no idle time. We present two new heuristics, a dispatch rule and a greedy procedure, and also consider the best of the existing dispatch rules. Both dispatch rules use a lookahead parameter that had previously been set at a fixed value. We develop functions that map some instance statistics into appropriate values for that parameter. We also consider the use of dominance rules to improve the solutions obtained by the heuristics. The computational results show that the function-based versions of the heuristics outperform their fixed value counterparts and that the use of the dominance rules can indeed improve solution quality with little additional computational effort.scheduling, early/tardy, heuristics, dispatch rules, dominance rules

Beam search algorithms for the early/tardy scheduling problem with release dates

In this paper we consider the single machine earliness/tardiness scheduling problem with di?erent release dates and no unforced idle time. We present several heuristic algorithms based on the beam search technique. These algorithms include classical beam search procedures, with both priority and total cost evaluation functions, as well as the filtered and recovering variants. Both priority evaluation functions and problem-specific properties were considered for the filtering step used in the filtered and recovering beam search heuristics. Extensive preliminary tests were performed to determine appropriate values for the parameters used by each algorithm. The computational results show that the recovering beam search algorithms outperform their filtered counterparts in both solution quality and computational requirements, while the priority-based filtering procedure proves superior to the rules-based alternative. The beam search procedure with a total cost evaluation function provides very good results, but is computationally expensive and can therefore only be applied to small or medium size instances. The recovering algorithm is quite close in solution quality and is significantly faster, so it can be used to solve even large instances.scheduling, early/tardy, beam search, heuristics

Fermentative bio-hydrogen production from organic wastes and sugars

Utilization of renewable energy has been identified as a priority within the “European Energy Policy” which stresses the need to develop new sources of green energy. A follow-up of the programme “Intelligent Energy – Europe” (Decision No. 1230/2003/EC of the European Parliament and of the Council of 26 June 2003) is projected for the 7th Framework Programme (2007-2013). The main focus of the programme is the production of electricity from renewable sources of energy, as described in Directive 2001/77/EC of the European Parliament and of the Council of 27 September 2001. According to this document, Portugal has committed to raise the national electricity production exclusively from renewable sources to 39% by 2010. In addition, it constitutes an essential part of the package of measures necessary to comply with the commitments made by the EU under the 1997 Kyoto Protocol on the reduction of greenhouse gas emissions. Hydrogen is a CO2-neutral energy source with a very promising future as an alternative to fossil fuels for energy production. The treatment and disposal of wastes by conventional methods poses many problems throughout the world and may result in the consumption of energy. In addition, costs to dispose and treat wastes are escalating. Hydrogen can be produced, from undesirable waste products by bacterial fermentation, to generate electricity. The Centre for Biological Engineering at the University of Minho is studying bio-hydrogen production from organic wastes and sugars. The specific tasks of the project (FCT/POCI/ENR/57786/2004) include the utilization of different waste compositions from a real kitchen waste and sugars to produce and optimize H2 yields, methanogenesis inhibition strategies, design, construction and operation of batch and continuous lab scale reactors for mesophilic (37 °C), thermophilic (55 °C), and hyperthermophilic (70 °C) conditions. In addition, molecular ecology techniques are being used to study bacterial community dynamics in the different bioreactors, comparing the microbial communities developed at different temperatures and different OLR. One objective is to determine the optimal conditions to select the most important microorganisms involved in H2 production